The Smoot-Hawley Act of 1930, was conceived by two Senators: Willis C. Hawley and Reed Smoot with the solid purpose of  mitigating the consequences of the Great Depression. The idea was to protect the domestic economy by increasing the tariff of a wide number of imported goods in order to protect in particular farmers and workers.
The reason why this actually spread the effects of the Depression was because it increased tariff at a level that it made the international commerce more difficult and this certainly brought negative consequences. In addition to that, unemployment actually grew in the years after the Act was passed, due mainly to the weak production, which made the situation even worse.
